Olefin polymerization catalysts which consist of transition metal halogen compounds and organometallic compounds are generally known. It is also known that the activity of the catalyst is generally improved if the transition metal halogen compound is supported on a carrier. Since the presence of large amounts of carrier can have an adverse effect upon the properties of the resulting polymer, it is obviously desirable to have catalysts with activity levels high enough that the presence of the carrier in the polymer will not pose any significant problem.
U.S. Pat. No. 3,642,746 discloses that improved supported catalysts of that type can be obtained by pretreating a carrier, such as a magnesium dihalide with certain electron donors and then combining the pretreated carrier with the transition metal halogen compound.
The present invention is directed to a new alternative process for improving the productivity of magnesium dihalide-supported ethylene polymerization catalysts.